feat(studio): clearer store + channel switcher + approvals & welcome polish

- store: repair the filter dialog crash (a Spacer lived directly in
  AlertDialog.actions, which is an OverflowBar, not a Flex — it threw
  and rendered a broken dialog). Buttons now sit in a Row.
- store: promote the module-store manager from a bare icon to a
  labelled 'Add store' button, and fully localize the dialog (DE/EN).
- store: add a curated 'Suggested stores' shelf with one-click
  add/remove (first entry: Recl∆Im). Each suggestion is probed for
  reachability and shows 'not available yet' until its index is
  published, instead of failing only on click. Fail-open on network
  errors so a transient hiccup never hides a real store.
- sidebar: the channel pill is now a one-click channel switcher
  (menu with per-channel running state + active check; switching
  writes ~/.chain/current-channel, restarts the daemon, and Studio
  repoints to the new channel).
- approvals: lead the card with the human prompt ('what am I
  releasing?') and demote the flow/step id to a metadata line; clear
  fallback when the step left the prompt empty.
- welcome: tidy the docs grid into equal-height paired rows with a
  full-width trailing card for the odd one out.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/pages/store.dart

@@ -234,10 +234,15 @@ class _StorePageState extends State<StorePage> {
               onPressed: _openFilterDialog,
             ),
           ),
-          IconButton(
-            icon: const Icon(Icons.storefront_outlined, size: 18),
-            tooltip: 'Module stores',
-            onPressed: () => ChainStoresDialog.show(context),
+          Padding(
+            padding: const EdgeInsets.only(right: ChainSpace.sm),
+            child: OutlinedButton.icon(
+              icon: const Icon(Icons.add_business_outlined, size: 16),
+              label: Text(l.storesManagerButton),
+              onPressed: () => ChainStoresDialog.show(context),
+              style:
+                  OutlinedButton.styleFrom(visualDensity: VisualDensity.compact),
+            ),
           ),
           IconButton(
             icon: const Icon(Icons.refresh, size: 18),
@@ -1139,38 +1144,49 @@ class _FilterDialogState extends State<_FilterDialog> {
           ],
         ),
       ),
+      // A single Row is the one action child: AlertDialog wraps
+      // `actions` in an OverflowBar (not a Flex), so a bare
+      // `Spacer()` here throws — it needs a Flex parent. Nesting
+      // the buttons in a Row gives the Spacer a valid Flex
+      // ancestor and keeps Reset left / Cancel+Apply right.
       actions: [
-        TextButton(
-          onPressed: () {
-            setState(() {
-              _status = '';
-              _source = '';
-              _installedOnly = false;
-              // Reset puts `installableOnly` back to its default
-              // (on) — the operator hits Reset to escape a
-              // custom-filter state and expects the default view
-              // back, not an everything-including-planned view.
-              _installableOnly = true;
-            });
-          },
-          child: Text(l.storeFilterReset),
-        ),
-        const Spacer(),
-        TextButton(
-          onPressed: () => Navigator.pop(context, null),
-          child: Text(l.buttonCancel),
-        ),
-        FilledButton(
-          onPressed: () => Navigator.pop(
-            context,
-            _FilterOutcome(
-              status: _status,
-              source: _source,
-              installedOnly: _installedOnly,
-              installableOnly: _installableOnly,
+        Row(
+          children: [
+            TextButton(
+              onPressed: () {
+                setState(() {
+                  _status = '';
+                  _source = '';
+                  _installedOnly = false;
+                  // Reset puts `installableOnly` back to its
+                  // default (on) — the operator hits Reset to
+                  // escape a custom-filter state and expects the
+                  // default view back, not an everything-
+                  // including-planned view.
+                  _installableOnly = true;
+                });
+              },
+              child: Text(l.storeFilterReset),
             ),
-          ),
-          child: Text(l.storeFilterApply),
+            const Spacer(),
+            TextButton(
+              onPressed: () => Navigator.pop(context, null),
+              child: Text(l.buttonCancel),
+            ),
+            const SizedBox(width: ChainSpace.sm),
+            FilledButton(
+              onPressed: () => Navigator.pop(
+                context,
+                _FilterOutcome(
+                  status: _status,
+                  source: _source,
+                  installedOnly: _installedOnly,
+                  installableOnly: _installableOnly,
+                ),
+              ),
+              child: Text(l.storeFilterApply),
+            ),
+          ],
         ),
       ],
     );